Senescent changes in human [unreadable] vision have been well documented, but the factors responsible for these changes [unreadable] are only partially understood. The proposed research is intended to provide [unreadable] fundamental data on aging of the human visual system using psychophysical [unreadable] methods that separate the relative contributions of optical and neural [unreadable] mechanisms. Because much of the sensitivity loss of cone pathways occurs at [unreadable] early stages of processing, we will examine age-related losses in cone [unreadable] photopigment optical density in the central 10 degree of retina for normal and [unreadable] sex-linked dichromats whose genes have been sequenced to look for genetic [unreadable] correlates of photopigment optical density and receptor "longevity." It is [unreadable] hypothesized that senescent changes in cone photopigment density will not be [unreadable] uniform with retinal eccentricity, and the outcome of this experiment will be [unreadable] important for theoretical and practical reasons. A second aim of the proposed [unreadable] research is to quantify senescent changes in the temporal properties of [unreadable] isolated color mechanisms through measurements of the temporal contrast [unreadable] sensitivity function and the impulse response function. The third aim is to [unreadable] determine senescent changes in spatial properties of isolated color mechanisms [unreadable] through measurements of the area of complete spatial summation (Ricco's area). [unreadable] Age-related changes in spatial summation are predicted based on our previous [unreadable] work, and documented losses of retinal ganglion cells with age, but we do not [unreadable] know whether this will be found in all color pathways. The fourth aim is also [unreadable] concerned with spatial properties of rod and cone pathways, but will measure [unreadable] spatial contrast sensitivity functions for isolated mechanisms. The final aim [unreadable] is based on our previous work showing that, at a perceptual level, the visual [unreadable] system employs mechanisms that compensate, in part, for losses in sensitivity [unreadable] at lower levels. Color appearance mechanisms will be proved by measurements of [unreadable] age-related changes in chromatic perceptive fields over areas of retina [unreadable] associated with different relative losses of cones and ganglion cells. [unreadable] Sensitivity of isolated cone mechanisms and color appearance will be measured [unreadable] for individuals before and after cataract extraction and implantation of [unreadable] intra-ocular lenses. These experiments will provide new information on [unreadable] mechanisms that promote color constancy despite substantial variations in the [unreadable] retinal image due to lenticular senescence. Each of these alms will include [unreadable] detailed tests of individual younger and older observers, and measurement on [unreadable] selected conditions with a large group of individuals ranging in age from [unreadable] approximately 12 to 85 years. In addition to providing basic data on the aging [unreadable] visual system, the experiments will provide probes for models of how the visual [unreadable] system adapts and compensates for degradations in the optical and neural images [unreadable] that occur with senescence and disease.